Abstract

The Arthur River area is situated on the north-west coast of Tasmania The rocksoutcropping in the area are correlates to the Proterozoic metasedimentary sequences of theRocky Cape Group. The Rocky Cape group and its correlates dominate the geology of thenorth western region of Tasmania, but are however, relatively under studied.The major part of this study involved a detailed analysis of the sedimentology in the ArthurRiver area, and from this a depositional model was constructed. A comparison of theseresults with the Rocky Cape Group 'type-section' is also presented. A minor part of thisresearch was structural mapping, which outlines the structural history of the area.Sedimentological studies showed that the Arthur River area contained three separate facies:a laminated carbonaceous mudstone; quartzarenite; and interbedded siltstone facies. Theseare interpreted to have been deposited in: a deep, low energy, reducing slope environment;a high energy, shallow marine tidal dominated shelf environment and; a moderate to lowenergy, outer shelf environment situated above storm wave base, respectively. Interestingsedimentary structures found within these rocks included: guttercasts in facies 1 and 3 andmudcracks in facies 3. The formation of the mudcracks was most probably due to theprocesses of diastasis.When the facies were combined into one depositional basin model, it was shown that thepalaeo-shoreline of this basin section was striking in a NW -SE direction. The tidalpalaeocurrent signature was parallel to this, forming a longshore tidal current system.The main structure of the area fits with the regional trends outlined for the westerncorrelates of the Rocky Cape Group. Dominant folding is in the NW-SE direction (Fl),with minor folding in the NE-SW direction (F2). Faulting in the area may also be related tothese stress fields.

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